This ^^^ is accurate. Most of the time, these dome lamps are on a circuit that includes a capacitor(inside our Body Control Module or BCM), so when the car is shut off and we go inside, the capacitor provides power for a few extra seconds until it runs out (hence why most of these lights fade to off slowly). The LED bulb requires less power for the same amount of light as a traditional bulb, so it eats the power from that capacitor slower and fades slower. My truck used to do this, and the Volvo still does to this date. After a half hour both would be completely dark though.Maybe due to the fact that the power sent to dim the normal bulb is still more than an LED needs so it takes longer to consume it?